1. What to look at in fire engineering analysis
Jamie Vistnes Manager, Fire Safety Policy Unit

2. Approaches and Methods of Analysis
Absolute
Comparative
Qualitative
Quantitative
Deterministic
Probabilistic 2

3. 1.2.9.4 Methods of analysis There are many forms of analysis methods:
formulas, equations and hand calculations
spreadsheet calculations
statistical studies
experiments with physical scale models
full-scale experimental tests such as fire tests or trial evacuations of real buildings
computer simulation of fire development and smoke spread
computer simulation of people movement. 3

4. 1.2.9.4 Methods of analysis The methods chosen should:
be well documented (especially their limitations and assumptions) either in the literature or by the fire engineer
be well validated
be suitable for the task
generate outputs that can be compared with the acceptance criteria agreed for the analysis
have clearly defined limitations and assumptions that are well documented.
“The FEB report should record, as appropriate, the above information for each method chosen.” 4

5. 1.2.9.4 Methods of analysis http://www.nist.gov/el/fire_grants.cfm
These can be summarised as needing to be:
Well documented and well validated
Suitable for the task
Used within limitations and assumptions
Generate suitable outputs to address acceptance criteria 5

6. Well Documented and Well Validated
Standards available for assessing and verifying fire models
ATS —2006
ISO/TR :1999
Australian Technical Specification
Guidelines—Fire safety engineering
Part 3: Assessment and verification of
mathematical fire models
ASTM E , Standard Guide for Evaluating the Predictive Capability of
Deterministic Fire Models 6

7. input parameters supplied to the model are inaccurate;
A.6 Review of FRIEDMAN, R., An International Survey of Computer Models for Fire And Smoke, Journal of Fire Protection Engineering, 4, pp , 1992
Reasons why a model may not yield results in complete accord with actual fire behaviour are:
idealizations and simplifications on which the model is based deviate significantly from reality;
input parameters supplied to the model are inaccurate;
"default" values of coefficients used internally in the model are incorrect;
the computation process yields a wrong result (due to poor choice of time steps or mesh size or due to mathematical singularities or instabilities);
the experimental measurements are incorrect or non-repeatable. 7

8. A.6 Review of FRIEDMAN, R., An International Survey of Computer Models for Fire And Smoke, Journal of Fire Protection Engineering, 4, pp , 1992
It is generally risky to apply a model to conditions which are drastically different from those for which the model has been validated.
Conclusion:
Just because a model exists, doesn’t mean it is necessarily accurate and appropriate for use. 8

9. Well Documented and Well Validated
How much effort goes in to reviewing validation and verification documentation?
How much effort goes in to investigating whether it even exists?
How much of this review is then documented in the FEB/FER? 9

10. Well Documented and Well Validated
FDS may be considered generally well validated for predicting smoke movement in a building.
Can also be used to predict fire spread and sprinkler operation
Questions still remain as to how accurately are these predicted.
Therefore, just because something is included in a model, doesn’t mean it can always be used. 10

11. Suitable for task
Some typical examples not considered suitable for the task:
Egress modelling may be undertaken to demonstrate that the evacuation time is short compared to the FRL prescribed, however these times do not correlate.
Fire Brigade Intervention is often analysed and quantified (to some extent), however not linked to the acceptance criteria
Whilst quantitative modelling and robust technical analysis is encouraged, it needs to be appropriate to the agreed acceptance criteria and not used as a “smoke screen” to fill out the report. 11

12. Within Limitations and Assumptions
How well do you know the limitations and assumptions of a tool?
Have you looked at the basis for deriving the tool?
For example, fire severity calculations derived from experiments in relatively small compartments.
When is it OK to move outside these limitations?
For example, using a zone model for a 2,500m2 compartment?
Again, are these clearly documented in the FEB/FER? 12

13. Generate suitable outputs to address acceptance criteria
Can the results generated be used to demonstrate that the acceptance criteria has been achieved?
Without sufficient outputs:
The conclusions drawn from the analysis cannot be appropriately documented
Makes it difficult for a reviewer to determine how much engineering judgement has been used 13

14. Use of Technical Tools - Inputs
Obviously affect the outcome – so critical
FRNSW experience a general lack of detail in FEB, therefore how can we agree
Need to further work on what are considered critical to the analysis
All inputs/assumptions clearly justified and documented
Also often find changes occur between FEB and FER, but not documented
Note: New Zealand Verification Method not considered an appropriate reference as this is a VM for an different country’s building code with no specific supporting references 14

15. Use of Technical Tools - Inputs
Sensitivities need to be considered, which may vary according to the tool being used
These should also be identified at FEB stage
FRNSW experience a wide variation in how this is considered 15

16. Use of Technical Tools - Outputs
Need to be sufficient to justify the results/conclusions made
FRNSW experience a wide variation in both what outputs are shown and how they are used, for example:
No results, only reference to modelling being undertaken
A random sample of CFD results provided that may not directly correlate with times concerned
CFD results at certain locations only
A full set of CFD results for each criteria and time of interest
Only thermocouple readings 16

17. Use of Technical Tools
Most frequent “technical tool” used is arguably the fire engineer themselves!
More development in models, less use in practice?
Is this because of the types of issues being addressed by fire engineering, or fire engineers changing methods of analysis to reduce costs? 17

18. What is Needed for the Future?
Encourage more robust quantitative analysis using technical tools, rather than qualitative comparisons to obscure DtS designs that are far from what is proposed
Full probabilistic risk assessments utilising technical tools to determine the risk
Individual and societal risk likely to drive policy development / direction in the built environment
AFAC part of BCC working group in this space
Wider consultation likely to occur
Quantifiable risk likely to be the underpinning structure on which building codes developed – need for proper risk assessment 18

19. Jamie Vistnes Manager - Fire Safety Policy Unit
Questions
Jamie Vistnes Manager - Fire Safety Policy Unit
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